// Rob McIntosh China JavaScript Document

	/********************************************************************
	 * Function:    emailCheck                                          *
	 * Description: This function verifies that the user has entered a  *
	 *              valid e-mail address.                               *  
	 ********************************************************************/

	function emailCheck (emailStr) {

		/* The following variable tells the rest of the function whether or not
		to verify that the address ends in a two-letter country or well-known
		TLD. 1 means check it, 0 means don't. */

		var checkTLD=1;

		/* The following is the list of known TLDs that an e-mail address must end with. */
		
		var knownDomsPat=/^(com|net|org|edu|int|mil|gov|arpa|biz|aero|name|coop|info|pro|museum)$/;

		/* The following pattern is used to check if the entered e-mail address
		fits the user@domain format. It also is used to separate the username
		from the domain. */
		
		var emailPat=/^(.+)@(.+)$/;

		/* The following string represents the pattern for matching all special
		characters. We don't want to allow special characters in the address.
		These characters include ( ) < > @ , ; : \ " . [ ] */
		
		var specialChars="\\(\\)><@,;:\\\\\\\"\\.\\[\\]";

		/* The following string represents the range of characters allowed in a
		username or domainname. It really states which chars aren't allowed.*/
		
		var validChars="\[^\\s" + specialChars + "\]";

		/* The following pattern applies if the "user" is a quoted string (in
		which case, there are no rules about which characters are allowed
		and which aren't; anything goes). E.g. "jiminy cricket"@disney.com
		is a legal e-mail address. */
		
		var quotedUser="(\"[^\"]*\")";

		/* The following pattern applies for domains that are IP addresses,
		rather than symbolic names. E.g. joe@[123.124.233.4] is a legal
		e-mail address. NOTE: The square brackets are required. */
		
		var ipDomainPat=/^\[(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})\]$/;

		/* The following string represents an atom (basically a series of non-special characters.) */
		
		var atom=validChars + '+';

		/* The following string represents one word in the typical username.
		For example, in john.doe@somewhere.com, john and doe are words.
		Basically, a word is either an atom or quoted string. */
		
		var word="(" + atom + "|" + quotedUser + ")";

		// The following pattern describes the structure of the user
		
		var userPat=new RegExp("^" + word + "(\\." + word + ")*$");
		
		/* The following pattern describes the structure of a normal symbolic
		domain, as opposed to ipDomainPat, shown above. */
		
		var domainPat=new RegExp("^" + atom + "(\\." + atom +")*$");
		
		/* Finally, let's start trying to figure out if the supplied address is valid. */
		
		/* Begin with the coarse pattern to simply break up user@domain into
		different pieces that are easy to analyze. */
		
		var matchArray=emailStr.match(emailPat);

		if (matchArray==null) {
			/* Too many/few @'s or something; basically, this address doesn't
			even fit the general mould of a valid e-mail address. */
			
			alert("Email address seems incorrect (check @ and .'s)");
			return false;
		}
		
		var user=matchArray[1];
		var domain=matchArray[2];

		// Start by checking that only basic ASCII characters are in the strings (0-127).
		
		for (i=0; i<user.length; i++) {
			if (user.charCodeAt(i)>127) {
				alert("Ths username contains invalid characters.");
				return false;
			}
		}
		for (i=0; i<domain.length; i++) {
			if (domain.charCodeAt(i)>127) {
				alert("Ths domain name contains invalid characters.");
				return false;
			}
		}

		/* if the e-mail address is at an IP address (as opposed to a symbolic
		host name) make sure the IP address is valid. */
		
		var IPArray=domain.match(ipDomainPat);
		if (IPArray!=null) {
			// this is an IP address
			for (var i=1;i<=4;i++) {
				if (IPArray[i]>255) {
					alert("Destination IP address is invalid!");
					return false;


				}
			}
			return true;
		}

		// Domain is symbolic name. Check if it's valid.
		var atomPat=new RegExp("^" + atom + "$");
		var domArr=domain.split(".");
		var len=domArr.length;
		for (i=0;i<len;i++) {
			if (domArr[i].search(atomPat)==-1) {
				alert("The domain name does not seem to be valid.");
				return false;
			}
		}

		/* domain name seems valid, but now make sure that it ends in a
		known top-level domain (like com, edu, gov) or a two-letter word,
		representing country (uk, nl), and that there's a hostname preceding
		the domain or country. */
		
		if (checkTLD && domArr[domArr.length-1].length!=2 &&
			domArr[domArr.length-1].search(knownDomsPat)==-1) {
			alert("The address must end in a well-known domain or two letter " + "country.");
			return false;
		}
		
		// Make sure there's a host name preceding the domain.
		if (len<2) {
			alert("This address is missing a hostname!");
			return false;
		}
		
		// If we've gotten this far, everything's valid!
		return true;
	}